Optimized Matching Of Combustion System On Single Cylinder Air-cooled Common Rail Diesel Engine

Most of Non-road single-cylinder diesel engines which are subject to simple structure and low price are equipped with naturally aspirated intake system and mechanical fuel injection system.With increasing emphasis on pollution and stricter emission regulations of non-road diesel engine in China,especially the non-road diesel engine ChinaⅣemission standard which will requires the emission control zones will be implemented in 2020.The emission tested modes are extended from point to zone modes when the emission type approval is applied.Therefore,the technologies need to be upgraded urgently for non-road diesel engines.The electronic controlled fuel injection system could provide superior fuel injection parameters for diesel engine under a wide range of working conditions,especially electronic controlled common rail fuel injection systems.The updating of the fuel injection system must involve optimal matching with intake system and combustion chamber.The relation of fuel（fuel injection rate,fuel space distribution）,air（intake flow,air motion）and combustion chamber（geometry and size）is need to optimized match to achieve good performances of diesel engine.In this paper,the 192F single-cylinder air-cooled diesel engine is taken as the research object.Based on the electronic controlled common rail fuel system set by the previous works of the research team,the optimization matching research among the intake system,combustion chamber and fixed fuel system is carried out.The main research contents and conclusions are as follows:（1）According to characteristics of common rail fuel injection system which are higher fuel injection pressure,smaller nozzle hole diameter and more nozzle hole numbers,the helical channel was cut off to reduce the swirl intensity in order to match the low swirl intensity produced by the helical intake port.The test was carried out on a steady flow test bench and the constant pressure difference method was used.The test results showed that the average Ricardo swirl ratio of improved helical intake port decreased by 14.37%compared to the original helical intake port,and the average flow coefficient increased by 11.52%.（2）Based on reading a large amount of references and researching parameters of the high pressure common rail fuel injection system,the structures of the lip,the bowl and the central convexity platform were redesigned to form new combustion chamber compared with the original combustion chamber matched with the mechanical fuel injection system.（3）Using AVL Fire software and simulation method,optimizing match research was carried out by adjusting the structural parameters and adopting single variable method.The combustion process and emissions characteristic were analyzed on different geometry,diameter-depth ratio,and bowl volume（compression ratio）of combustion chamber.From the air motion velocity field,the fuel to air equivalence ratio and the temperature field of the combustion process etc.,combined with in-cylinder combustion characteristics and emissions formation,the results showed that the structures of the circular dent,the arc lip and the ball top central convexity platform were beneficial to reducing the airflow motion dead zone and promoting the quality of fuel to air mixing,increasing the diameter-depth ratio and compression ratio within appropriate range was beneficial to reducing fuel spray impinging on the wall,improving fuel atomization quality and improving fuel to air mixing quality which were help for effectively organizing combustion process and reducing post combustion.（4）Based on the optimization of the combustion system and fuel injection parameters of the192F common rail diesel engine,the performance and emissions were tested adopting the steady-state 8 modes emissions test cycle.The CO,HC+NO_x and PM brake specific emissions were 3.58,5.87 and 0.35 g·（kW·h）^-1,which has a large margin of deterioration compared with non-road diesel engine present ChinaⅢand future ChinaⅣemission regulation.The optimizing works achieve the expected results.